The present invention relates generally to an electro chemical plating (ECP) process, and more particularly to an additive used in the same.
As semiconductor technology continues to advance, integrated circuit (IC) components, such as transistors and chip interconnect wirings, continue to shrink in size. These IC components become small enough, such that the processing speed is very sensitive to intrinsic resistance and capacitance of the interconnect wirings. As such, high conductive materials are the popular choices for the interconnect wirings. Many of these high conductive metals are quickly replacing aluminum which was once widely used for IC's interconnections. The speed of interconnect is affected by resistance and capacitance of the conductive materials used. Resistance and capacitance of the conductive materials, such as copper and aluminum, have a trade off relationship, such that chip makers can give up more resistance for lower capacitance, or vice versa. For example, copper with a lower resistivity may lead indirectly to a capacitance advantage. For identical line dimensions, copper and aluminum provide similar capacitance, but copper has a lower resistance. Similarly, for copper and aluminum of equivalent resistance, copper lines can be thinner and exhibit lower capacitance. Thus, copper is now one of the most popular materials for conducive lines in the IC technology.
However, when copper is used in the IC, issues such as oxidation occurs. Unlike aluminum whose initial oxidation layer helps form a protective layer preventing further oxidation, copper can oxidize indefinitely. This oxidation problem can lead the copper based interconnects into an unreliable state, causing many problems in the future. In order to keep this from happening, additives are added in the electro chemical plating solution in the ECP process. The additives can also provide several other functions, such as acceleration, suppression, and leveling. A popular choice of materials used for these additives is polymer, a chemical compound or mixture of compounds formed by polymerization and consisting essentially of repeating structural units. Most of the conventional polymer additives have a relatively high impurity density. This raises the stress applied onto the copper based interconnects and may lead to disturbance of the leveling effect. The higher stress created by the additives of high impurity density increases the chances of cracking of the copper based interconnects, thereby causing other integration problems.
What is needed is an additive used in the ECP process for producing the copper based structures with improved stress and leveling effects.